U.S. patent number 5,188,664 [Application Number 07/798,463] was granted by the patent office on 1993-02-23 for anti-coalescent ink composition and method for making the same.
This patent grant is currently assigned to Hewlett-Packard Company. Invention is credited to Raymond J. Adamic, Theresa A. Gibney.
United States Patent |
5,188,664 |
Adamic , et al. |
February 23, 1993 |
Anti-coalescent ink composition and method for making the same
Abstract
An improved ink composition having an additive therein for
reducing the surface tension of the composition and increasing the
drip mass per firing. Reduced surface tension and increased drop
mass per firing enable the production of graphic images having
enhanced clarity and contrast while avoiding problems such as
bubble adhesion/longevity and ink mottling/coalescence. The
additive basically consists of at least one polyether polyol. The
additive is usable in a wide variety of ink compositions. In a
preferred embodiment, ink compositions using the additive will
include about 0.001-1.0% by weight additive (0.0075%=optimum). The
resulting ink formulations are capable of printing high resolution
graphic images while avoiding the problems described above.
Inventors: |
Adamic; Raymond J. (Corvallis,
OR), Gibney; Theresa A. (Corvallis, OR) |
Assignee: |
Hewlett-Packard Company (Palo
Alto, CA)
|
Family
ID: |
25173468 |
Appl.
No.: |
07/798,463 |
Filed: |
November 26, 1991 |
Current U.S.
Class: |
106/31.58;
347/100 |
Current CPC
Class: |
C09D
11/30 (20130101) |
Current International
Class: |
C09D
11/00 (20060101); C07D 011/02 () |
Field of
Search: |
;106/20,22 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Hewlett-Packard Journal, vol. 39, No. 4 (Aug. 1988). .
Hewlett-Packard Journal, vol. 36, No. 5 (May 1985). .
The Flexible Polyurethane Foam Handbook, Dow Chemical USA, Midland,
Mich..
|
Primary Examiner: Bell; Mark L.
Assistant Examiner: Klemanski; Helene
Claims
The invention that is claimed is:
1. A method for manufacturing a reduced surface tension ink
composition having an increased drop mass per firing comprising the
steps of:
obtaining a supply of at least one chemical dye; and
combining said chemical dye with at least one polyether polyol in
order to produce said ink composition, said polyether polyol having
physical characteristics sufficient to enable said ink composition
to have a reduced surface tension and increased drop mass per
firing compared with an ink composition produced in the absence of
said polyether polyol.
2. The method of claim 1 wherein said polyether polyol has an
average molecular weight of about 3000, about 56 --OH groups, and a
viscosity of about 225 cks at 100.degree. F.
3. The method of claim 1 wherein said ink composition comprises
about 0.001-1.0% by weight said polyether polyol.
4. The method of claim 1 wherein said ink composition comprises
about 0.5-20.0% by weight said chemical dye.
5. A method for manufacturing a reduced surface tension ink
composition having an increased drop mass per firing comprising the
steps of:
obtaining a supply of at least one chemical dye; and
combining said chemical dye with at least one polyether polyol in
order to produce said ink composition, said composition comprising
about 0.001-1.0% by weight said polyether polyol, and about
0.5-20.0% by weight said chemical dye, said polyether polyol having
physical characteristics sufficient to enable said ink composition
to have a reduced surface tension and increased drop mass per
firing compared with an ink composition produced in the absence of
said polyether polyol, said polyether polyol having an average
molecular weight of about 3000, about 56 --OH groups, and a
viscosity of about 225 cks at 100.degree. F.
6. An ink composition having a reduced surface tension and an
increased drop mass per firing comprising:
at least one chemical dye; and
at least one polyether polyol combined with said chemical dye in
order to produce said ink composition, said polyether polyol having
physical characteristics sufficient to enable said ink composition
to have a reduced surface tension and increased drop mass per
firing compared with an ink composition produced in the absence of
said polyether polyol.
7. The composition of claim 6 wherein said polyether polyol has an
average molecular weight of about 3000, about 56 --OH groups, and a
viscosity of about 225 cks at 100.degree. F.
8. The composition of claim 6 wherein said composition comprises
about 0.001-1.0% by weight said polyether polyol.
9. The composition of claim 6 wherein said composition comprises
about 0.5-20.0% by weight said chemical dye.
10. An ink composition having a reduced surface tension and an
increased drop mass per firing comprising:
at least one chemical dye; and
at least one polyether polyol combined with said chemical dye in
order to form said composition, said composition comprising about
0.001-1.0% by weight said polyether polyol and about 0.5-20.0% by
weight said chemical dye, said polyether polyol having physical
characteristics sufficient to enable said ink composition to have a
reduced surface tension and increased drop mass per firing compared
with an ink composition produced in the absence of said polyether
polyol, said polyether polyol having an average molecular weight of
about 3000, about 56 --OH groups, and a viscosity of about 225 cks
at 100.degree. F.
11. A method for printing a stable image onto a substrate
comprising the steps of:
providing an ink composition having a reduced surface tension and
an increased drop mass per firing, said ink composition comprising
at least one chemical dye and at least one polyether polyol
combined with said chemical dye, said polyether polyol having
physical characteristics sufficient to enable said ink composition
to have a reduced surface tension and increased drop mass per
firing compared with an ink composition produced in the absence of
said polyether polyol;
providing a printing apparatus;
supplying said printing apparatus with said ink composition;
activating said printing apparatus in order to cause said apparatus
to apply said ink composition onto said substrate; and
allowing said ink composition on said substrate to dry in order to
produce said image thereon.
12. The method of claim 11 wherein said polyether polyol has an
average molecular weight of about 3000, about 56 --OH groups, and a
viscosity of about 225 cks at 100.degree. F.
13. The method of claim 11 wherein said printing apparatus
comprises a thermal inkjet printing system.
14. The method of claim 11 wherein said composition comprises about
0.001-1.0% by weight said polyether polyol.
15. The method of claim 11 wherein said ink composition comprises
about 0.5-20.0% by weight said chemical dye.
16. A method for printing a stable image onto a substrate
comprising the steps of:
providing an ink composition having a reduced surface tension and
an increased drop mass per firing, said ink composition comprising
about 0.5-20.0% by weight of at least one chemical dye and about
0.001-1.0% by weight of at least one polyether polyol, said
polyether polyol having physical characteristics sufficient to
enable said ink composition to have a reduced surface tension and
increased drop mass per firing compared with an ink composition
produced in the absence of said polyether polyol, said polyether
polyol having an average molecular weight of about 3000, about 56
--OH groups, and a viscosity of about 225 cks at 100.degree.
F.;
providing a printing apparatus;
supplying said printing apparatus with said ink composition;
activating said printing apparatus in order to cause said apparatus
to apply said ink composition onto said substrate; and
allowing said ink composition on said substrate to dry in order to
produce said image thereon.
17. The method of claim 16 wherein said printing apparatus
comprises a thermal inkjet printing system.
Description
BACKGROUND OF THE INVENTION
The present invention generally relates to printing technology, and
more specifically to the production and use of ink compositions
having chemical additives therein which substantially improve print
quality.
Significant developments have been made in the field of electronic
printing technology. Specifically, a wide variety of highly
efficient printing systems currently exist which are capable of
dispensing ink in a rapid and accurate manner. Thermal inkjet
systems are especially useful for this purpose. Thermal inkjet
printing cartridges basically include an ink reservoir in fluid
communication with a substrate having a plurality of resistors
thereon. Selective activation of the resistors causes thermal
excitation of the ink and expulsion thereof from the ink cartridge.
Representative thermal inkjet systems are discussed in U.S. Pat.
No. 4,500,895 to Buck et al.; U.S. Pat. No. 4,513,298 to Scheu;
U.S. Pat. No. 4,794,409 to Cowger, et al.; the Hewlett-Packard
Journal, Vol. 36, No. 5 (May 1985); and the Hewlett-Packard
Journal, Vol. 39, No. 4 (August 1988), all of which are
incorporated herein reference.
Notwithstanding the existence of advanced printing systems,
additional research has also been conducted in order to produce new
and effective ink products to be used in these systems. Unless ink
compositions are properly formulated, problems can occur with
respect to ink delivery and image quality. These problems are
especially acute in cartridge systems which do not include a foam
or sponge-type reservoir system for holding ink therein. For
example, it is important for ink products to be specially
formulated so that the surface tension levels thereof are not
excessively high. Ink compositions having excessively high surface
tension levels (e.g. +60 dynes/cm) often produce graphics having a
low degree of quality and resolution. In addition, applied ink
compositions having high surface tension values may mottle or
coalesce on the paper or other print media being used, thereby
causing blotchy images. Ink compositions having high surface
tension values frequently promote bubble adhesion/longevity within
the firing chambers of thermal inkjet cartridges and other printing
systems. Bubble adhesion/longevity involves the formation of
bubbles in the ink which do not dissipate or dissipate at a slow
rate. This problem again results in impaired cartridge
operation.
In an attempt to control the above problems, surfactants have been
added to the ink compositions. Exemplary surfactant materials
suitable for this purpose include polyethylene glycol;
N,N-Dimethyldodecyl amine-N-oxide;
3-(N,N-Dimethylpalmityl-ammonio)-propanesulfonate, and a
commercially available product from the Air Products Company of
Philadelphia, Pa. sold under the trademark Surfynol 465 which has
the following structure: ##STR1##
While surfactants decrease the surface tension of ink compositions,
they do not necessarily control other problems which may occur
during application of the compositions. For example, lowering the
ink surface tension generally has no predictable effect on steady
state ink drop mass per firing. The phrase "ink drop mass per
firing" as used herein basically involves the amount of ink ejected
from a nozzle in an ink cartridge during one firing thereof, and is
a function of many variables. These variables include but are not
limited to the geometry of the firing chamber in the cartridge, the
resistor design used in the cartridge, the cartridge input energy,
the designated firing frequency, and the physio-chemical properties
of the ink materials (e.g. ink wettability).
Decreasing the surface tension of ink compositions does not
necessarily effect drop mass per firing because the other factors
indicated above may play a more significant role. Ink compositions
with a low drop mass per firing are delivered to print media in an
insufficient quantity, resulting in low contrast images. This
occurs because the amounts of chemical dyes and other important
materials in these compositions are insufficient to cover the
desired areas of the print media to produce clear, dark images.
Accordingly, a need remains for an ink composition which is
specifically formulated to have a low surface tension level while
maintaining a high level of ink drop mass per firing. The ink
composition should also be suitable for use in a wide variety of
printing systems, including thermal inkjet units. The present
invention satisfies these needs in a unique and effective manner,
as described herein below.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved ink
composition and method for making the same.
It is another object of the invention to provide an improved ink
composition which has a reduced surface tension in order to prevent
ink coalescence/mottling on print media.
It is a further object of the invention to provide an improved ink
composition which has a high drop mass per firing so that a proper
amount of ink will be delivered during printing.
It is a further object of the invention to provide an improved ink
composition which is formulated to avoid excessive bubble
adhesion/longevity within printing cartridge systems.
It is a still further object of the invention to provide an
improved ink composition which uses a minimal number of chemical
components.
It is a still further object of the invention to provide an
improved ink composition which is easily formulated using readily
available chemical components.
It is an even further object of the invention to provide an
improved ink composition which is readily dispensed using a wide
variety of printing systems.
It is an even further object of the invention to provide an
efficient method for printing using the ink composition described
herein.
In accordance with the foregoing objects, the present invention
involves an improved ink composition and methods for making/using
the same. The ink composition and methods described herein are
highly effective in producing clear and stable printed images while
avoiding coalescence/mottling. The composition basically consists
of one or more selected dye materials in combination with other
ingredients including but not limited to solvents, buffers,
biocides, kogation-reducing agents, metal chelating agents, and the
like. As indicated above, ink compositions having excessively high
surface tension levels and a low drop mass per firing frequently
cause numerous problems. In order to reduce the surface tension and
increase the drop mass per firing of the ink compositions, a
surface tension reducing agent having a structure capable of
accomplishing these goals is added to the ink compositions. This
agent consists of a polyether polyol composition described in
greater detail below.
The selected polyether polyol is preferably added to each ink
composition so that the composition contains about 0.001-1.0% by
weight polyether polyol (about 0.0075% by weight=optimum). This
relatively small amount of polyether polyol simultaneously performs
a variety of important functions in the completed ink composition.
First, it reduces the surface tension of the ink composition.
Second, it increases the drop mass per firing of the ink
composition. Third, by decreasing the surface tension of the ink
composition, ink bubble adhesion/longevity within printing
cartridges (e.g. thermal inkjet units) is substantially reduced or
eliminated. All of these items result in improved print quality
without physical modification of the ink cartridges or printing
units. Accordingly, the present invention represents a significant
advance in the art of printing technology/ink formulation and
satisfies a long-felt need for efficient and versatile ink
compositions.
These and other objects, features, and advantages of the invention
will be described below in the following Detailed Description of
Preferred Embodiments.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention involves a specially-formulated ink
composition which avoids print quality problems associated with
high surface tension (e.g. ink mottling/coalescence), low drop mass
per firing, and excessive bubble adhesion/longevity within the
firing chambers of thermal inkjet cartridges and the like. The
composition is unique and may be used in a wide variety of printing
systems including those which do not include foam-based ink
reservoirs.
In order to produce an ink composition in accordance with the
invention, one or more dyes are first selected. Exemplary dye
materials (as well as other ink components) are described in
co-owned U.S. Pat. No. 4,963,189 to Hindagolla which is
incorporated herein by reference. It should be noted that the dye
materials and other chemical agents listed herein and in the
foregoing issued U.S. Patent are for example purposes only. Thus,
the present invention shall not be limited to the ink components
described below, and is prospectively applicable to a wide variety
of the other ink compositions known in the art.
Dye materials suitable for use in the present invention as
described in U.S. Pat. No. 4,963,189 have the following basic
structure: ##STR2##
In this structure, there should be at least two COOH groups
(2-4=preferred), with the number of COOH groups being equal to or
greater than the number of SO.sub.3 H groups. It is also preferred
that at least two of the COOH groups be attached directly to an
aromatic carbon atom.
In a dye molecule wherein X=H, W may be in the ortho, meta, or para
position with respect to the azo (--N.dbd.N--) group, with W
preferably being in the para position. However, it is preferable
that X=COOH, and that a dye molecule incorporating two COOH groups
have such groups in the 3,5-, 3,4-, or 2,5-, position relative to
the azo group.
It is also preferred that dye molecules having the above basic
structure do not include more than two SO.sub.3 H groups, and that
the ultimate number of COOH groups in the dye molecule exceed the
number of SO.sub.3 H groups. Specific and exemplary dye structures
are provided in Table I below:
TABLE I ______________________________________ Dye # X W Y Z R
______________________________________ 1 3-COOH 5-COOH H H H 2
3-COOH 5-COOH COOH H H 3 3-COOH 5-COOH H COOH H 4 3-COOH 5-COOH H
SO.sub.3 H H 5 3-COOH 5-COOH SO.sub.3 H H H 6 H 4-COOH H COOH H 7
3-COOH 4-COOH H H CH.sub.2 COOH 8 2-COOH 5-COOH H SO.sub.3 H
CH.sub.2 COOH 9 3-COOH 5-COOH SO.sub.3 H H CH.sub.2 COOH 10 3-COOH
5-COOH H H CH.sub.2 CH.sub.2 COOH 11 3-COOH 5-COOH H COOH CH.sub.2
COOH ______________________________________
In a preferred embodiment, the ink compositions of the present
invention should comprise about 0.5-20% (optimum range=about 1-10%)
by weight dye (whether one dye or a combination of dyes is used).
It is also desirable to use at least two different dyes to form the
ink compositions described herein. The use of multiple dyes offers
numerous benefits, including (1) the reduction of cartridge nozzle
clogging; (2) the reduction of cartridge "bearding" (i.e. ink
crystallization); (3) greater pH flexibility; (4) greater control
of ink hue; and (5) the reduction of ink "bronzing" (i.e.
reddish-brown discolorization). When multiple dyes are used, the
ratio of dyes to each other may be in any proportion. However, if
multiple dye mixtures are used, each dye included therein should
not comprise less than 10% by weight of the total dye mixture.
The dyes described above are preferably used in salt form.
Exemplary dye salts may consist of alkali metal salts (e.g.
Na.sup.+, K.sup.+ or Li.sup.+ salts), ammonium salts, or
substituted ammonium salts. These salts are formed by mixing a dye
in acid form with a stoichiometric amount of a selected base in
water.
In order to prepare the completed ink compositions, a suitable
solvent must be used in combination with the selected dye
materials. In a preferred embodiment, the completed ink
compositions should include about 2-30% by weight water-soluble
organic solvent. Exemplary water-soluble organic solvents suitable
for this purpose include but are not limited to C.sub.1 -C.sub.4
aliphatic alcohols (e.g. methanol, ethanol, n-propanol,
isopropanol, n-butanol, sec-butanol, tert-butanol, or isobutanol),
amides (e.g. formamide or dimethylacetamide), ketones/ketone
alcohols (e.g. acetone or diacetone alcohol), ethers (e.g.
tetrahydrofuran or dioxane), nitrogen-containing heterocyclic
ketones (2-pyrrolidone, N-methyl-pyrrolid-2-one, or 1,3
dimethylimidazolid-2-one), polyalkylene glycols (e.g. polyethylene
glycol or polypropylene glycol), alkylene glycols and thioglycols
containing C.sub.2 -C.sub.6 alkylene groups (e.g. ethylene glycol,
propylene glycol, butylene glycol, triethylene glycol,
thiodiglycol, hexylene glycol, and diethylene glycol), glycerol,
1,2,6-hexanetriol, and lower alkyl ethers of polyhydric alcohols
such as 2-methoxyethanol, 2-(2-methoxyethoxy)ethanol,
2-(2-ethoxyethoxy)ethanol, 2-methoxy-2-ethoxy-2-ethoxyethanol,
2-[2-(2-methoxyethoxy)ethoxy]ethanol, 2-[2-(2-ethoxyethoxy)ethoxy]
ethanol.
In the foregoing group of solvents, preferred materials include
glycols and glycol ethers (e.g. ethylene glycol, diethylene glycol,
triethylene glycol, or 2-methoxy-2-ethoxy-2-ethoxyethanol),
polyethylene glycols with molecular weights of up to 500, and
heterocyclio ketones (e.g. 2-pyrrolidone, N-methylpyrrolid-2-one or
1,3-dimethylimidazolid-2-one). Preferred solvent mixtures includes
a binary mixture of water and diethylene glycol or a binary mixture
of water and 2-pyrrolidone.
It may also be desirable to add one or more buffers to the ink
compositions so that a pH operating range of about 7-9.5 is
maintained. Higher pH levels normally reduce ink clogging in
cartridges and ink bronzing. In a preferred embodiment, the ink
composition will include about 0.1-5.0% by weight buffer solution.
Exemplary buffers should have a pK of about 6.5-10 and may include
but are not limited to TES
(N-tris[hydroxymethyl]methyl-2-aminoethanesulfonic acid), BICINE
(N,N-bis[2-hydroxyethyl]glycine), TEA (triethanolamine), TRIS
(tris[hydroxymethyl]aminomethane), BORAX (sodium borate
decahydrate), and combinations thereof.
Biocides may also be optionally used in the ink compositions
described herein in order to control microbial growth. In a
preferred embodiment, the completed ink compositions will include
about 0.1-0.5% by weight biocide. Exemplary biocides suitable for
this purpose would include products sold under the names PROXEL.TM.
GXL and PROXEL.TM. CRL by Imperial Chemical Industries of
Manchester, England. These materials include
1,2-benzisothiazolin-3-one as the key active ingredient in
combination with dipropylene glycol.
In addition, a selected optional phosphate may be added to the ink
in order to control problems associated with "kogation". Kogation
involves the build-up of residue known as "koga" on the resistors
of thermal inkjet printing systems after the repeated operation
thereof. This residue impairs printer operation. Both monobasic
(H.sub.2 PO.sub.4.sup.-) and dibasic (HPO.sub.4.sup.-2) phosphate
materials may be used. A variety of different cations may be
associated with the phosphate, including but not limited to
ammonium. In a preferred embodiment, the phosphate concentration in
the completed ink composition would range from about 0.005-0.5% by
weight (about 0.07%=optimum).
Finally, an optional metal chelating agent may be added to the
completed ink composition. The chelating agent is designed to
control or eliminate the formation of undesired precipitates within
ink cartridges. Tests have shown that inks prepared using carboxyl
dyes as described herein contain various metal ions, including
calcium, iron, and magnesium. Metal precipitates often form within
the cartridge, thereby resulting in clogging of the cartridge,
improper firing, and/or incorrect drop size. To control this
problem, chelating agents are used in the ink composition which
bind with extraneous metal ions and form metal complexes. As a
result, the metal ions are unavailable to form precipitates within
the cartridges. Exemplary chelating agents include but are not
limited to ethylenediaminetetraacetic acid (EDTA), malonic acid,
and salicylic acid. In a preferred embodiment where a chelating
agent is used, the completed ink composition should contain about
0.01-0.5% by weight chelating agent (about 0.1%=optimum).
An example of a completed ink composition suitable for use in
accordance with the present invention is as follows:
EXAMPLE 1
______________________________________ Component Wt. %
______________________________________ Dye structure #1 (Table 1)
1.1 Dye structure #4 (Table 1) 1.1 Solvent (2-pyrrolidone) 7.5
Buffer BORAX 0.2 TRIS 0.2 Phosphate anion (ammonium phosphate) 0.07
Chelating agent (EDTA) 0.1 Biocide (PROXEL .TM. GXL) 0.3 water
89.43 100.00 ______________________________________
This ink composition has a pH of about 8.5, a viscosity of about
1.3 cps, a surface tension of about 65 dynes/cm, a conductivity of
about 8 mS/cm, and an absorbance maximum at about 575 nm.
The ink compositions described herein generally have a relatively
high surface tension (e.g. between about 60-70 dynes/cm). A high
surface tension within the range described above offers certain
advantages, including the promotion of a capillary interaction
between the fluid ink materials and firing chamber surfaces of the
selected ink cartridge. A high degree of capillary action leads to
rapid and efficient ink refilling between subsequent firings in the
cartridge chamber.
However, in many cases, a high surface tension can also present
problems which greatly offset the foregoing advantages. For
example, the use of ink compositions having high surface tension
values may produce poorly-defined graphic images in which the ink
is not evenly distributed over the print media (e.g. paper). This
type of situation is commonly known as ink "mottling" or
"coalescence". High surface tension levels cause mottling or
coalescence to occur because of interactions between the ink
compositions and media surface which prevent the compositions from
becoming evenly distributed thereon. This is especially true with
respect to graphic images which include large regions of solid
printed images.
A further problem caused by increased surface tension levels is the
formation of small ink bubbles within the firing chamber of the
selected ink cartridges. Such bubbles have a high degree of
adhesion/longevity as defined above. This phenomenon impairs
cartridge operation and degrades print quality. Lower surface
tension levels minimize bubble adhesion/longevity.
As noted above, the reduction of ink surface tension levels has
been accomplished using various surfactants including but not
limited to those listed above. However, tests have shown that
surfactants cannot successfully control another problem
characteristic of ink compositions known as "low drop mass per
firing". As indicated above, drop mass per firing (usually
expressed in nanograms) is basically defined as the amount of ink
ejected from a given firing chamber of a specific ink cartridge for
a given amount of input energy at a particular frequency. Many
variables control drop mass per firing, including but not limited
to the specific ink composition involved, the type of printing
system being used to deliver the ink, and the other factors listed
above. In particular, surface tension and the ink wettability (e.g.
the ability of ink to spread out on the surface of a substrate),
have a substantial effect on drop mass per firing. Regarding the
ink compositions described herein, as well as most commercially
available ink compositions, the drop mass per firing typically
ranges from about 100-200 ng (nanograms) with respect to most
commercially available cartridge systems (e.g. those referenced
herein).
The present invention involves a special additive which is
tremendously effective in controlling all of the foregoing
problems. This additive consists of a compound selected from a
group of materials known conventionally as "polyether polyols." As
described in Sections 3.1 and 3.2 of The Flexible Polyurethane Foam
Handbook by the Dow Chemical Company of Midland, Mich.
(incorporated herein by reference), a polyether polyol chemically
consists of a poly-functional alcohol which includes a polymeric
chain having a plurality of ether (C--O--C) linkages. More
specifically, according to The Flexible Polyurethane Foam Handbook,
supra, a polyether polyol is a "polymeric reaction product of an
organic oxide and a compound containing two or more active hydrogen
atoms." The hydrogen atom-containing compounds are conventionally
known as "initiators."
Organic oxides used to produce polyether polyols typically consist
of epoxides (cyclic three-membered rings) examples of which include
but are not limited to ethylene oxide, propylene oxide,
1,2-butylene oxide, and epichlorohydrin. Exemplary initiators
include but are not limited to water, ethylene glycol, 1,2
propylene glycol, glycerine, trimethylolpropane, ethylene diamine,
pentaerythritol, diethylene triamine, sorbitol, and sucrose.
By way of example, a representative polyether polyol may be
prepared in accordance with the following reaction: ##STR3##
However, a wide variety of polyether polyols may be produced,
depending on the type of organic oxide and initiator being used.
Thus, the above reaction sequence is only a single, representative
example of what type of product can be produced using selected
initiators and organic oxides.
Most commercially available polyether polyols are proprietary, and
their exact structures are not available to the public. In
addition, in view of the significantly complex configurational
characteristics of polyether polyols, many if not most commercial
products have structures which are literally unknown in terms of
exact structural configuration. Thus, polyether polyols are often
best defined in terms of their physical characteristics such as
average molecular weight, viscosity, number of --OH groups,
etc.
A polyether polyol having physical characteristics capable of
effectively accomplishing the objectives of the present invention
as defined herein is commercially available from the Dow Chemical
Company of Midland, Michigan under the trademark VORANOL.RTM. 3010.
The structural configuration of this material is not presently
known and/or available for the reasons described above. However,
this polyether polyol (as well as other polyether polyols) is best
represented by the physical characteristics thereof. With respect
to VORANOL.RTM. 3010 (a triol), these characteristics are: 1)
number of --OH groups=about 56; 2) average molecular weight=about
3000; 3) viscosity=about 225 cks at 100 degrees F; 4) specific
gravity=about 1.016; 5) maximum % water=about 0.06; and 6) flash
point=about 221 degrees C.
In a preferred embodiment, the completed ink composition will
contain about 0.001-1.0% by weight polyether polyol (about
0.0075%=optimum). The polyether polyol is preferably added to the
ink composition in the form of a stock solution having a
concentration level of about 10-20% by weight polyether polyol in a
solvent preferably consisting of one of the water-soluble organic
solvents listed above which are used to produce the ink
compositions described herein. These solvents include but are not
limited to glycols and glycol ethers (e.g. ethylene glycol,
diethylene glycol, triethylene glycol, or
2-methoxy-2-ethoxy-2-ethoxyethanol), polyethylene glycols with
molecular weights of up to 500, and heterocyclic ketones (e.g.
2-pyrrolidone, N-methylpyrrolid-2-one or
1,3-dimethylimidazolid-2-one). However, the present invention shall
not be limited to the use of any particular stock solution
concentration level or type.
The use of polyether polyol is widely applicable to numerous ink
formulations/dyes including those listed above and other
compositions known in the art. Tests have shown that the addition
of polyether polyol to ink compositions of the type described
herein typically reduces the surface tension thereof by about
25-30%. Thus, an ink composition having a surface tension of about
65 dynes/cm would consequently have a surface tension of about 45
dynes/cm after polyether polyol addition.
As noted above, various surfactants have been used in the past to
control surface tension levels in ink compositions. However, the
use of these materials does not result in a corresponding increase
in drop mass per firing. In contrast, the desired result occurs
when polyether polyol is added. Specifically, the surface tension
is lowered and the drop mass per firing is increased, typically by
about 10-20%. For example, if a specific ink composition has a drop
mass per firing of about 125 ng, this value will increase to about
140 ng after the addition of polyether polyol within the range
presented above.
The polyether polyol additive described herein is of substantial
value in that it is capable of simultaneously solving three
problems, namely, (1) excessively high surface tension levels; (2)
low drop mass per firing; and (3) excessive ink bubble
adhesion/longevity within the firing chambers of the ink cartridges
being used. As a result, higher quality graphic images are formed
while avoiding problems associated with ink coalescence and
cartridge clogging. In addition, all of these benefits are
accomplished using very small amounts of polyether polyol.
Ink compositions using polyether polyol may be delivered using a
wide variety of printing systems, including but not limited to
thermal inkjet units as described in U.S. Pat. No. 4,500,895 to
Buck et al.; U.S. Pat. No. 4,513,298 to Scheu; U.S. Pat. No.
4,794,409 to Cowger, et al.; the Hewlett-Packard Journal, Vol. 36,
No. 5 (May 1985); and the Hewlett-Packard Journal, Vol. 39, No. 4
(August 1988). The ink compositions are conventionally supplied to
a selected printing system which is then activated in order to
deliver the compositions onto a substrate. After being allowed to
dry (which occurs rapidly in the case of nearly all commercially
available ink compositions), a stable printing image is produced
with a high degree of clarity and contrast.
By using polyether polyol as described herein, a balance between
proper surface tension values, proper drop mass per firing, and
desired cartridge performance is achieved. Specifically, both drop
mass per firing and general cartridge performance are improved
simultaneously, which has yet to be achieved when other additives
are used. Accordingly, the developments described herein represent
a tremendous and substantial advance in the art of ink manufacture.
In addition, as previously indicated, the polyether polyol additive
of the present invention is prospectively usable in a wide variety
of ink compositions known in the art. For illustration purposes,
Example 2 provided below lists a representative ink formulation
comparable to the formulation of Example 1 which incorporates a
polyether polyol additive:
EXAMPLE 2
______________________________________ Component Wt. %
______________________________________ Dye structure #1 (Table 1)
1.1 Dye structure #4 (Table 1) 1.1 Solvent (2-pyrrolidone) 7.5
Buffer BORAX 0.2 TRIS 0.2 Phosphate anion (ammonium phosphate) 0.07
Chelating agent (EDTA) 0.1 Biocide (PROXEL .TM. GXL) 0.3 polyether
polyol (VORANOL .RTM. 3010) 0.0075 water 89.4225 100.00
______________________________________
This ink composition has a surface tension of about 45 dynes/cm
compared with about 65 dynes/cm in the formulation of Example 1
which did not include a polyether polyol additive. In addition, the
composition of Example 2 has an average drop mass per firing of
about 130-145 ng (when delivered using a conventional thermal
inkjet printing system) compared with a drop mass per firing of
about 120-125 ng in the formulation of Example 1.
Finally, tests were conducted involving an ink composition having a
variety of surfactants and the polyether polyol of the present
invention added thereto. The specific ink composition which was
used consisted of the components listed in Example 2 except for the
substitution of various individual surfactants. In each test, the
ink composition contained about 0.0075% by weight surfactant or
polyether polyol. Identical thermal inkjet delivery systems were
used to deliver the inks (e.g. of the type listed in U.S. Pat. No.
4,794,409 to Cowger et al. without a foam-type reservoir). The test
results are as follows:
TABLE II ______________________________________ surface tension
approximate Ink additive (dyn/cm) drop mass (ng)
______________________________________ none 65.0 120 polyethylene
glycol 58.8 121 Surfynol 465 .TM. 54.1 123 N,N Dimethyldodecyl 38.7
125 amine-N-oxide 3-(N,N Dimethylpalmityl- 38.3 126
ammonio)-propanesulfonate polyether polyol 45.7 132 (VORANOL .RTM.
3010) ______________________________________
As indicated in Table II, the polyether polyol and surfactants all
reduced the surface tension of the ink composition. However, the
polyether polyol also provided a substantial increase in drop mass
per firing which was not evident with respect to the surfactants.
Thus, the data in Table II clearly illustrates the multiple
benefits accomplished through the addition of polyether polyol as
described above.
Having herein described preferred embodiments of the present
invention, it is anticipated that suitable modifications may be
made thereto by individuals skilled in the art which remain within
the scope of the invention. Thus, the present invention shall only
be construed in accordance with the following claims:
* * * * *